280 FRESH- WATER RHIZOPODS OF NORTH AMERICA. ' 



motion. Not unfrequently spindle-like accumulations of protoplasm occur 

 in the course of the pseudopodal threads. Sometimes, through the conjunc- 

 tion and spreading of several of the latter together, islet-like expansions 

 occur, and become the centres of secondary nets. 



The pseudopodal extensions of Grornia consist of pale granular proto- 

 plasm with coarser and more defined granules. The latter are observed to 

 be in incessant motion along the course of the threads, flowing in opposite 

 directions in all except those of the greatest delicacy. See fig. 4. In the 

 larger threads, the granules are immersed and near together; in the smallest 

 threads, they are in single rows, more or less widely separated, and thicker 

 than the threads, so that these appear like strings of minute beads. 



In the flow of the granules in the pseudopodal threads, they are some- 

 times seen to slacken their speed, or for a moment become stationary, and 

 then reverse their course. Granules arriving at a dividing branch are 

 sometimes retarded, and then take one or another direction; or, passing from 

 one main branch to another through a by-path, they may take a reverse 

 course from their former one. 



The movements of the granules, though apparently independent, are 

 rather due to the currents or flow of the protoplasm constituting the basis 

 of the pseudopodal threads. 



Besides the granules, minute vacuoles often make their appearance 

 along the course of the pseudopods. Some of these seem to be of the 

 character of contractile vesicles, — starting as mere points, slowly enlarging, 

 and then collapsing. Other circular spots in the pseudopodal threads, or 

 in patches formed by union and anastomosis of the latter, appear as mere 

 circular spaces, due to spreading of the protoplasm in the meshes of the net. 



Occasionally, minute diatoms and other objects which come within the 

 territory of the pseudopodal net of Gromia terricola are seen to become 

 immersed in the substance of the threads, and to move along in a manner 

 reminding; one of a boat carried along* in the current of a river. 



Gromia terricola, by means of its pseudopodal net, was observed to be 

 strongly disposed to accumulate around it a quantity of dirt, and especially 

 at the posterior part of the body, as seen in fig. ] . In one individual, after 

 completely surrounding itself with sand and dirt, it entirely withdrew its 

 pseudopodal rays, and nothing that was done could induce the animal again 

 to protrude them. . 



